1. Field of the Invention
The present invention relates to a fiber reinforced resin assembly.
2. Description of Related Art
Fiber reinforced resin assemblies are widely used as structural components, in industrial and leisure applications. These assemblies are generally supplied as a prepreg. Prepreg materials comprise a fibrous reinforcement phase together with a matrix resin comprising one or more resinous materials, one or more curing agents and optionally other additives such as accelerators, tougheners, flame retardants, fillers and the like forming together a so-called matrix resin. The matrix resin can generally be cured at temperatures in the range from 50° C. to 200° C.
The period of time in which a prepreg remains handleable with properties intact outside the specified storage environment, normally a cold store or freezer, is called out-time or out-life. Known prepregs have limited out-life in their uncured state at room temperature. This is particularly evident in low temperature cure thermoset matrix resin compositions where the curing agents used to achieve cure at these low temperatures, typically between 50 and 100° C., react with the resins even at ambient temperatures. For example, a matrix resin composition consisting of an epoxy resin and an imidazole curing agent that can be cured at 60° C., can have a room temperature stability of less than two days rendering it unusable thereafter. Stability during storage at ambient temperatures is important, especially if materials are to be transported long distances, and/or stored at ambient temperatures before use. It is, of course, possible to store these known prepregs at temperatures below room temperature to enhance their shelf-life, but the need for large or expensive refrigeration units can make this option undesirable.
For certain applications it is desirable that assemblies have an out-life of at least two weeks; this is particularly true where the assemblies find utility in sports applications, and more particularly in the ski/snowboard industry. Furthermore, it is desirable that the assembly has a certain degree of tack. Tack, which is a measure of the adhesion of a prepreg ply to the tool surfaces or to other prepreg plies in the assembly, is an adhesion characteristic of the matrix resin that is controlled in order to facilitate ply cutting and lay-up operations. The plies should be capable of being removed and repositioned if necessary. For application in the ski/snowboard industry the assembly ideally has a tack level that is almost dry to touch, but the resin is flexible enough to permit the material to be wound around mandrels without cracking. The term “leathery” is sometimes used to describe such a tack level. Several tests are available that can be used for semi-quantitative measurement of tackiness. One such test uses a Meedus Datatac Analyser. This instrument consists of a sensor head assembly that contains a precision load cell, which converts the tack force on eight sensor probes into an electric signal. A control console accepts this signal and processes it into stored analogue and digital peak values.
Attempts have been made to prolong the out-life of assemblies of the kind referred to herein. For example, U.S. Pat. No. 2,999,834 refers to the application of a composition comprising a polymerization catalyst embedded into a fibrous reinforcement. The matrix resin is then applied to the fibrous reinforcement in situ such that the curing reaction occurs. The catalyst is delivered to the fibrous reinforcement as a dispersion or solution and therefore must not react with or initiate a reaction of the solvent/dispersal medium. This clearly limits the nature of the catalyst that can be delivered in this way, which in turn limits the nature of the matrix resin. U.S. Pat. No. 2,999,834 also refers to the application of a composition comprising the matrix resin and the catalyst to a fiber reinforcement provided with a catalyst accelerator. In this instance the curing reaction is instantaneous and thus the out-life of the assembly is not prolonged.
EP 0424833 B1 refers to application of a metathesis catalyst to a substrate. The substrate is then placed in a mold and a monomer composition is applied to the substrate such that a curing reaction occurs.
U.S. Pat. No. 3,666,615 refers to a composite sheet material comprising a thermosetting resin layer and a hardening agent layer whereby the two layers are separated by a contact preventative film that melts when heated. A fiber base is embedded in either of the two layers to provide structural support for the composite. Thereby the room temperature out-life of the assembly is prolonged. However, the use of such a barrier film requires using a film of a different type from the thermosetting resin, which complicates the system and increases the costs and the time involved in producing the composite.